Was Canada right to change its breast screening guidelines? No

Changes to breast cancer screening guidelines have been big news since the release of the Canadian Task Force on Preventive Health Care’s (CTFPHC) updated guidelines in December. Women 50 to 74 year old are now recommended to undergo screening mammography every two to three years, while women 40 to 49 are advised not to undergo screening and not to examine their breasts, regardless of breast tissue density.

But patients must wade through the recommendations with caution — here’s why.

Adoption of the new breast cancer update is projected to result in over 400 Canadian lives lost each year. Incredibly, these new guidelines were issued without the involvement of an expert in breast diagnosis or treatment. Instead, the panel involved family doctors, nurses, a chiropractor, an occupational therapist and a nephrologist (kidney specialist).

Why? The Task force claimed that including an expert in breast cancer diagnosis would bias the guideline development. The Task Force implied that because radiologists earn a living by diagnosing breast cancer they place financial gain above the welfare of patients.

As a physician who lost a loved one to breast cancer, and as a mother, friend and colleague to many women affected by breast cancer, I find this particularly galling, and many of my colleagues in Canada agree.

A recent study from Sweden published in the journal, Cancer showed that screening mammography resulted in 60 per cent fewer deaths from breast cancer over a 20-year time period. Another recent study published in Cancer shows after 30 years, screening mammography and advances in treatment have averted nearly 615,000 deaths from breast cancer in the U.S. alone since 1989.

A Canadian study of over 2 million women screened for breast cancer over 20 years showed that women 50 to 70 had a 40 per cent reduction in breast cancer mortality, and women 40 to 49 had a 44 per cent lower rate of dying from breast cancer when they participated in screening mammography.

The CTFPHC issued its 2018 guidelines without including these important studies and focused instead on a 30-year-old Canadian National Breast Screening (CNBSS) study that had been previously discounted in 2002 by the World Health Organization due to poor quality mammography and poor study design. A breast cancer expert on the panel would have avoided this error.

The Task Force focused on harms of screening. They cited an estimate of overdiagnosis of 41 per cent of breast cancers. No credible expert in screening correctly estimates overdiagnosis to be more than 10 per cent, a number that has been substantiated by the Swedish screening trials. The 41 per cent is based on the outdated and discredited CNBSS study. A breast cancer expert on the panel would have been able to point this out.

The Task Force also focused on the harms of false positives from screening mammography. They estimated the rate of false positives to be 30 per cent. Wrong again. Canadian database statistics available online for free demonstrate the annual abnormal recall rates for each province and territory for screening mammography. The numbers are consistent — less than 10 per cent. A breast cancer expert on the panel would have been able to point out the error of this calculation.

And the task force did not consider one of the most significant harms of screening — the harm of a missed diagnosis or false negative. Several studies show that women who are not screened or detected at an early stage have a much higher rate of dying from breast cancer.

Women with dense breast tissue have a much higher chance of being detected late with breast cancer, often after it has spread to the lymph nodes, because the cancer may be masked by their dense breast tissue. The Task Force ignored this evidence and did not consider the added risk of dense breast tissue in their guidelines. A breast cancer expert on the panel would have been aware of this harm.

Now, over 44,000 Canadians have signed a petition asking for these flawed guidelines to be opposed.

What needs to happen now?

The
federal health minister should reject the task force guidelines. A new
task force should be convened that includes experts of breast cancer
screening mammography. And the Canadian task force should update the
breast cancer screening guidelines to include evidence from recent
observational trials and actual Canadian data on screening mammography.
To do less than this would be to fail Canadian women and their families.